Particularly, the present invention refers to a type of burner wherein the outflow port, or ports, for feeding the pilot flame with a gas-primary air mixture is disposed, or are disposed, over the radial outlets adapted to feed the main flames with such a gas-primary air mixture. Such an outflow port is particularly shaped to direct the pilot flame towards the outlets of the main flames, so as to allow the ignition of the latter. Such a burner, responding to a particular normative prescription of some countries, further provides that the outflow port for the pilot flame and the radial outlets for the main flames are realized, at least partially, in the so-called flame spreader, that is, in its turn, closed by a top lid.
It has to be observed that with “flame spreader” is usually meant an annular element provided with, at least partially on its perimeter wall, cuttings or holes, providing the gaseous fluid outflow. Such an annular element is an outer side wall of a transit chamber of the gas-primary air fuel mixture in a burner, so as to define a flame crown of the burner itself. The flame spreader, according to a known art, may be realized as a different piece, or otherwise may be obtained in one piece with the burner body.
Domestic burners having the outflow port, or ports, for feeding the pilot flame, placed over the radial outlets for feeding the main flames, are known.
For example, the European Patent Application EP-A-0945679, in the name of GAZ DE FRANCE, teaches to realize an outflow port for a pilot flame, placed over the main flames, obtained between the upper surface of a flame spreader and the lower surface of the corresponding lid.
More particularly, the GAZ DE FRANCE Patent Application teaches to obtain some prominences (i.e. studs), reciprocally spaced, between the upper lid and the corresponding flame spreader, which are placed over a plurality of outlets of the gas-primary air mixture for the main flames, and extend only partially for the whole thickness of the flame spreader, such that, upstream of such a prominences, an annular slit (opening) between the flame spreader itself and the corresponding lid is obtained. Such prominences allow the passing of a predetermined amount of the gas-primary air fuel mixture into such an annular slit (opening), which generates, once ignited, a laminar pilot flame being able to cause the ignition of the main flames below.
Such a burner has however some drawbacks. Indeed, because the outflow port for the pilot flame is placed over the plurality of the outlets for the main flames, the gas-primary air mixture outflow through the exit opening for feeding the pilot flame may be particularly irregular and unstable, above all during the ignition step of the pilot flame itself, or in the ignition transitory of the main flames. The Applicant has experimentally verified that, straight after the combustion spark by the ignition spark plug, a series of thermo-fluid-dynamic events developing around the region of the combustion spark will not allow to obtain an appropriate gas-primary air mixture exchange through the outflow port. Substantially the pilot flame is not fed adequately during the ignition transitory, thereby resulting irregular, with the drawback that the primary flame ignition is compromised too.
In addition, in the case of a burner provided with more flame concentric crowns, that is provided with two or more flame spreaders, the combustion instability found in single flame crowns leads to a non-contemporary, and difficult, ignition of every primary flame of such crowns of burner flames.
Object of the present invention is to realize a burner of the type afore illustrated, that allows to stabilize the pilot flame combustion at least during the ignition step thereof, and then during the ignition of the main flames, as well as to stabilize the combustion itself of the gas-primary air mixture of the main flames during the burner use.
A further object of the present invention is to realize a burner that, in case it is provided with more flame crowns, will guarantee a substantially contemporaneous ignition and a more efficient combustion of the main flames present in each flame crowns, even if igniting, by an apposite ignition spark plug, only one crown of main flames of the burner.